Human rights watchdog Amnesty International says more than 100 prominent musicians have signed an open letter calling for the release of jailed members of the Russian feminist punk performance art collective Pussy Riot.

Amnesty said on July 22 that Adele, U2, Madonna, Yoko Ono, Bruce Springsteen, Paul McCartney, and Sting were among those who signed the letter.

The musicians urged Russian authorities to free 23-year old Nadezhda Tolokonnikova and 25-year-old Maria Alyokhina, who received two-year sentences last August for protesting against President Vladimir Putin in Moscow's main cathedral.

Their parole appeal hearings are scheduled later this week.

The letter, organized by Amnesty International, says the impact of Pussy Riot's "shockingly unjust trial and imprisonment has spread far and wide, especially among your fellow artists, musicians, and citizens around the world."